1. Field of the Invention
This invention relates to a fluid turbine structure which is used to generate power by exposure to wind, tidal or ocean currents.
2. Description of the Prior Art
With sources of energy, such as petroleum, natural gas and the like, being rapidly depleted throughout the world, either new sources of such energy must be found or alternative sources must be developed to fulfill the energy requirements for a highly technical society. Natural, non-polluting, inexhaustible sources of energy, such as the wind, the tides, and the ocean currents can fulfill these needs.
Many attempts have been made heretofore to convert kinetic energy in ambient wind fields or tidal currents into shaft rotational energy in either horizontal or vertical axis machines to generate power for diverse purposes. Typically, the horizontal axis machines are of the propeller type which have existed for centuries in various forms. A major drawback of the horizontal axis type machine is that the plane of blade rotation must constantly change as the wind changes direction. This is usually accomplished in practice by affixing a "tail" or vertical stabilizer to the rear of the rotor and allowing the rotational axis to pivot into the wind. This introduces undesirable gyroscopic loads and a design constraint in that the response of the machine to changes in wind direction must be sufficiently rapid to track and capture the available kinetic energy. Furthermore, the operation of such machines is highly inefficient.
For example, U.S. Pat. Nos. 2,153,523 and 2,177,801, each illustrate a horizontal axis machine which uses wind driven double impellers for simultaneously rotating the field and armature windings of an electrical generator in opposite directions to double power production. The windings of the generator are connected to coaxial shafts which are driven in opposite or counter rotation by oppositely curved wind impellers. The impellers have opposite curvatures so as to turn in opposite directions when positioned normal to the direction of the wind by a vane, "tail", or vertical stabilizer.
Twin impeller wind machines of this type have been able to provide more electrical power because of their inherent design. However, in the construction of horizontal, twin impeller wind machines, one impeller has always been placed behind the other in parallel, vertical planes. Accordingly, both impellers must get their energy from the same wind field while rotating in opposite directions causing undesirable gyroscopic forces on the machine, while causing drag of one impeller relative to the other slowing the tip velocity of the impellers and thereby creating inefficient power production. As previously stated, such a design also requires that the impellers be placed in a plane which is constantly changing as the wind direction changes and therefore must be rapid in response to changes in wind direction under the urging of the "tail" or vane.
Accordingly, in recent years, a number of vertical axis machines have been investigated as an alternative source of converting kinetic energy in ambient wind fields and tidal currents into shaft rotational energy. These include the Savonius, Darrieus and Gyromill configurations in which the impellers have taken the form of exposed air foils, sails, and paddles. Many of these rotor structures are inefficient because when they rotate away from the fluid source, they also must return to their starting point and therefore, must cut back into the source of fluid, which tends to retard their rotation, leading to inefficient power production.
Since the state of the art has not been satisfactory, other innovative approaches have recently been proposed. One approach has been to generate a vortical flow by introducing appropriate non-rotating structures in the flow and to attempt to capture some of the associated wind pressure energy in addition to the conversion of the ambient kinetic energy. Sforza, for example, has placed the rotational axis of a propeller type windmill coaxially with the core of a vortex generated by a delta wing at incidence to the wind, so that the turbine ingests the angular kinetic energy of the upstream vortex. Yen has investigated an alternate mode of vortex augmentation in which a confined vortex is generated in a tower, and a low-pressure core is used as a pump for a propeller type turbine flow to discharge into.
It will be appreciated from the foregoing discussion that fluid powered turbines have mainly been machines placed in fluid currents to rotate from the direct force of that current as it moves past a rotor or impeller that is connected to a power generator. Little has been done in the way of molding, shaping, directing, or increasing the velocity of the incoming fluid upon the rotor arrangement. In theory, the power available from a fluid current is proportional to the cube of the fluid current velocity. Therefore, the most powerful fluid driven machine would be one in which means are provided to increase the velocity of the arriving fluid and which is designed for maximum efficiency.
This suggests the desirability of a fluid energy machine incorporating the advantages of a vertical axis and flow-focusing housing or shroud. Ideally, only the housing would have to pivot to present the inlet to the oncoming fluid flow, thus eliminating any gyroscopic loads, as in horizontal axis machines, and greatly mitigating the problem of rapid response to wind directions shifts since the outer housing and tail could be constructed of lightweight materials and rotate relative to the rotor.
Such a device was described in detail in my prior U.S. Pat. No. 4,057,270, issued Nov. 8, 1977. The fluid turbine disclosed in that patent is characterized by increased power output and efficiency and is accomplished by providing upper and lower twin rotors which are spaced in parallel, horizontal planes so as to be subject to separate wind fields or fluid currents and, therefore, subject to independent operation. The rotor or impeller blades are not forced to cut back into the wind or fluid current as in the prior art devices, but rather the vector force of the fluid impinging on the blades and the vector force imparted by new fluid entering the rotor are complementary.
Two substantially annular, rotor housings are each provided with a plurality of radially extending blades connected to coaxial shafts. One of the shafts is connected to the field windings of an electrical generator, while the other shaft is connected to the armature windings. The radial blades in each rotor housing, when exposed to a fluid force, are adapted to rotate in opposite or counterdirections causing the field and armature windings of the generator to rotate in opposite directions to increase the power output from the generator.
A tail vane and "lazy susan" bearing connected to each housing provides means for keeping the machine pointed normal to or into the oncoming fluid. The housings rotate relative to the rotor blades thereby enabling the blades to rapidly respond to wind direction shifts.
Properly curved stator blades adjacent to the entrance to each rotor housing form a series of fluid jets which provide acceleration to the oncoming fluid and a means for directing that fluid in a manner normal to the path of rotation of the rotor blades. This has the effect of increasing the starting torque on the radial rotor blades about the annular housing of each opposite rotating rotor and once operation is commenced, to increase the available effective force of the incoming fluid current.
Directing fluid to the stator blades are two fluid scoops at 45 degree angles to the housings. The scoops placed in this manner increase the velocity of the fluid entering the entrance to each housing and stator apertures and results in increasing the force delivered upon each blade on both rotors which increases the velocity of both rotors in opposite directions and thus multiplies the power output by an extremely significant amount. New fluid passing through the stator jets formed by the stator blades will tend to recycle this fluid, changing its direction and thus adding to the force of the fluid already in the rotor housing. This increases the rotor torque. The stator jets bend the fluid from its normal position to a position aiding the internal fluid and applying pressure against the rotor blades making this internal fluid compatible with new fluid entering the housing to eliminate turbulence.
Tunnels are also mounted on the top of each rotor housing to deliver fluid to the interior of the housing and create a lower pressure area inside each housing to increase the velocity of the fluid within the housing and the pressure on the rotor blades. By use of the arrangement described, power output is available even in light fluid currents or winds, and in heavy currents power output is greatly multiplied.
While my prior device generated effective power, I discovered that at least the same amount of power could be generated in relatively light winds and at relatively low rotor tip velocities by the use of a single rotor structure and housing which is designed to further augment the fluid velocity impinging upon the rotor blades. The improved apparatus is disclosed in my co-pending application Ser. No. 876,217, filed Feb. 9, 1978.
That apparatus includes an additional fluid pathway into the rotor housing for directing fluid flow from a fluid source in such a way that incoming fluid impinges upon all of the rotor blades simultaneously at start up and during rotation. By enabling the fluid flow to impinge simultaneously on all of the rotor blades, the kinetic energy initially lost in starting the rotor moving is captured and used. Moreover, greater turning torque is established after rotation has commenced.
This increased efficiency is obtained while providing a housing surrounding the rotor blades which is independently rotatable relative to the rotor, thereby quickly enabling the rotor to face the oncoming fluid regardless of direction. The housing is designed to preclude the rotor blades from turning back into the resistance of the oncoming fluid.
Additional velocity augmentation devices are provided on the housing, including a downwardly directed frontal scoop which accelerates the ambient flow as it enters the housing as well as creating a low pressure area beneath the housing by blocking the flow. This low pressure area in conjunction with reflected flow provided in the housing can flush deenergized fluid from between the rotor blades out of the housing through fluid exit passages formed in the base of the housing to draw more fluid into the housing to impinge on the rotor blades.
The net-effect of such a structure is to increase both efficiency and power output enabling a single rotor (and therefore considerably less material) to furnish the same or better power than had heretofore been realized in my counter-rotating, double rotor machine, which is of critical importance in the field. For example, the unique flow focussing structure increases the power and efficiency of the rotor above the ideal efficiency (Betz limit) of unshrouded propeller type windmills. This efficiency as produced by the above-described turbine at extremely low rotor tip velocities; specifically, by comparison--at one-tenth the rotor tip velocity of the vertical Darrieus rotor with a simultaneous result of doubling the power output. This enables the turbine to achieve a higher exponential rate of power in high winds, than has ever been achieved heretofore, with low maintenance due to low centrifugal forces and bearing wear.